Pt Schottky diodes were fabricated on high-crystal-quality Al0.2Ga0.8N/GaN epitaxial films grown using epitaxial AIN/sapphire template (AlN template), and their current transport characteristics were measured and analyzed. It was confirmed that reverse leakage currents in Schottky diodes formed on AlN template were drastically reduced compared with samples on sapphire formed with a low-temperature buffer layer. The current transport characteristics in Schottky diodes formed on AIN template were found to be almost explicable using the thermoionic emission and tunneling current components, unlike with samples formed on sapphire. This indicates that the amount of unintentional impurity levels near the surfaces is extremely small for those high-crystal-quality Schottky diodes. Hydrogen-sensing characteristics were also investigated for a Pt/AlGaN/GaN Schottky diode formed on AIN template. The diode sensor exhibited sufficient changes in the reverse current even under exposure to extremely slight H-2 concentration of 50 ppm and exhibited clear reversible responses. These current changes seemed to be due to the reduction of the Schottky barrier height with H2 exposure. (c) 2007 American Vacuum Society.